CI: update the PR contents

Author: ForNeVeR

src/scripts/Update-Dependencies.ps1

@@ -134,7 +134,17 @@ if ($hasChanges)
     $($_.ReleaseNotes)
 "@
   }
-  $prBody = $updateReleaseNoteStrings -join "`n"
+  $prBody = @'
+# Maintainer Note
+> [!WARNING]
+> This PR will not trigger CI by default. Please close it and reopen manually to trigger the CI.
+>
+> Unfortunately, this is a consequence of the current GitHub Action security model (by default, PRs created by bots
+> aren't allowed to trigger other bots).
+
+The updates packages' release notes follow below.
+
+'@ + $updateReleaseNoteStrings -join "`n"
 }
 
 ApplyUpdates $updates